The Universal Mobile Telecommunication System (UMTS) describes a technical standard of third-generation radio communication network, which is defined by the Third Generation Partnership Project (3GPP). A UMTS network consists of a core network and an access network. The core network includes Circuit Switching (CS) or Packet Switching (PS) domains. The CS domain provides circuit-switched services, such as voice. The PS domain provides packet-switched services, such as Internet access.
Currently, in the Long Term Evolution (LTE)/System Architecture Evolution (SAE) technology, LTE is intended to provide a low-cost network that can reduce time delay, increase user data rates, and improve system capacity and coverage, and deliver PS domain services over IP networks. FIG. 1 illustrates the LTE/SAE network architecture and functions.
The Mobility Management Entity (MME) is designed to store User Equipment (UE) mobility management contexts, such as user identity, mobility management status, and location, to process Non Access Stratum (NAS) signaling, and to ensure the security of NAS signaling.
An SAE gateway (SAE GW) consists of two parts: Serving Gateway (S-GW) and Packet Network Gateway (P-GW). As two logical entities, S-GW and P-GW may exist as one or more physical entities.
The S-GW stores user plane contexts, such as a UE's IP address and routing information, monitors data for validity, and routes packet data. As an interface responsible for communication between the S-GW and MME, S11 exchanges information relating to UE mobility management and session control.
The P-GW, as a User plane anchor, is responsible for connecting UE to a packet data network. The entity implements packet routing and forwarding, policy and charging control, and user-specific packet filtering.
In existing 2G/3G networks and LTE/SAE networks as shown in FIG. 2, the first and second Routing Areas (RA) indicate RAs of existing 2G/3G networks. The UE will initiate a Routing Area Update (RAU) process when it changes RA. The UE will initiate network registration whenever it changes RAT, on which the UE camps. Frequent network registration processes due to this camped RAT change may cause a huge waste of air interfaces. The first, second, third and fourth Tracking Areas (TAs) describe the TAs of an LTE/SAE. When a multi-mode UE moves in a network and enters the first RA, to allow the network to page the UE within the RAT, the UE needs to register with the SGSN of the 2G/3G network. When entering the first TA, the UE needs to register with the MME of the LTE/SAE network. When moving from the first TA to the first RA, the UE needs again to register with the SGSN of the 2G/3G network. Consequently, frequent registrations may cause a considerable amount of registration signaling overload.
Within the framework of conventional technology, the UE can activate an Idle State Signaling Reduction (ISR) process, i.e. the UE first initiates an attach procedure and registers with the 2G/3G or SAE network. When moving from the SAE network or 2G/3G network or from the 2G/3G network to the SAE network, the UE needs to register with the other RAT, so that the UE registers with both access networks. Then, while moving within the registered RA or a TA of either network, the UE does not need to launch any registration process, except that the UE initiates periodical location update (RAU/TAU).
Before the ISR is activated, the UE only registers with the 2G/3G or SAE network. In this situation, two timers (periodical location update timer and Mobile Reachable Timer, MRT) are used to maintain the UE attach status.
When the UE is attached to a network, the UE retains a periodical location update timer, while the network retains an MRT. The MRT in the network is slightly longer than the periodical location update timer in the UE.
When the UE goes to idle mode or switches to another network, the network MRT and the periodical location update timer at the UE side starts from their initial values; when the UE goes to active mode, both the timers stop; when the periodical location update timer at the UE side expires, the UE will initiate a periodical location update process on the network.
If the network MRT receives no periodical location update message from the UE, the network can detach the UE in an implicit manner immediately or within a preset period of time, that is, the network will delete the UE's Mobility Management (MM) and Session Management (SM) contexts.
When the ISR is activated, the UE registers with both the 2G/3G and SAE network while it only camps on one RAT. In this situation, four timers—periodical UE location update timer for RAT1, periodical UE location update timer for RAT2, MRT timer for the first network RAT, and MRT timer for the second network RAT—are used to maintain the UE attach status.
If the periodical location update timer for RAT1, where the UE camps, expires, a location update procedure is initiated.
If the periodical location update timer for RAT1 expires, but the UE now camps on RAT2, the UE needs to record the expiry information relating to the periodical location update timer for RAT1 and update its location as soon as the UE moves back to RAT1.
When the UE camps on RAT2, the expiry of the periodical location update for RAT1 will not cause the UE to change its camped RAT or to initiate location update. When the network MRT for RAT1 expires, UE contexts will not be deleted. Instead, a longer timer 2 is started.
When the Timer 2 for RAT1 expires, the network will contact RAT2. When RAT2 agrees to detach the UE, the network will detach the UE in an implicit manner. When the MRT for RAT1 expires but Timer 2 for RAT1 does not expire, upon receiving downlink data, the S-GW will send downlink data notification. In this situation, the RAT Core Network (CN) node (MME or SGSN) relating to the expired MRT will not implement the paging process, because the UE does not camp on the RAT, then the RAT node (MME or SGSN) relating to said expired MRT returns downlink data notification to the S-GW.
The inventor has identified the following defects in the existing technology during the implementation of the present technology.
In an SAE network, if the ISR is not activated, and if the UE is idle and the MRT expires at MME or SGSN, the S-GW would still send downlink data notification to the MME to trigger MME paging when download data reaches the S-GW, as MME or S-GW is a separate node and the S-GW serves as the user plane termination point in the idle mode. However, the MME continuously returns Deny messages, thus causing signaling overhead and wasting network resources. If the ISR is activated, the S-GW needs to send downlink data notification to both the SGSN and MME, which triggers SGSN and MME to page UE. If the UE camps on RAT2 while the MRT for RAT1 expires; or if the UE camps on RAT1 while the MRT for RAT2 expires, for this idle UE, each time the S-GW receives download data, it will send signaling to the MME and SGSN, thus causing the RAT node (MME or SGSN) whose MRT expires to receive signaling continuously and return failure messages, which in turn may cause considerable overhead. In addition, if MRTs on both RAT nodes expire, the present invention provides no suitable mechanism to detach the UE in an implicit manner.